Methods for propagating microorganisms for fermentation &amp; related methods &amp; systems

ABSTRACT

Disclosed are compositions, methods, and systems for propagating microorganisms for fermentation.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.16/193,485 filed Nov. 16, 2018, which claims the benefit of U.S.Provisional Patent Application Ser. No. 62/587,310, filed Nov. 16, 2017,wherein the entirety of each application is incorporated herein byreference.

BACKGROUND

Propagating microorganisms, namely to increase the quantity of themicroorganisms, may be desirable for one or more reasons. For example,it may be desirable when the particular microorganism is expensive, forexample in transporting or storing, or when the microorganism can beused as feed or feed supplements.

Also desirable is the ability to use alternative, more accessible, ormore economical components in a propagation medium (e.g.,lignocellulosic material, and the like). However, the hydrolysis orbreak down of lignocellulosic materials can produce one or moreby-products that can inhibit enzymatic activity of enzymes, growth ofyeast and other microorganisms, and/or fermentation of monosaccharidesto a biochemical. Examples of such inhibitory compounds include aceticacid from ester hydrolysis of acetyl groups on xylan and lignin,phenolic compounds derived from lignin hydrolysis, and/or furfural and5-hydroxymethylfurfural (HMF), which can be produced by the dehydrationof pentoses and hexoses, respectively.

There is a continuing need to provide compositions, methods, and systemsto reduce inhibitors such as furfural and/or to be able to use suchcompositions for propagating microorganisms and for fermentation.

SUMMARY

Embodiments of the present disclosure include a method of propagating amicroorganism, the method including:

providing a lignocellulosic hydrolysate comprising at least onemonosaccharide and at least one inhibitor, where the at least oneinhibitor is at a first concentration, wherein the at least oneinhibitor is a byproduct of hydrolysis of lignocellulosic biomass, andwherein the at least one inhibitor is an inhibitor of fermentation bythe microorganism;

reducing the first concentration of the at least one inhibitor in aportion of the lignocellulosic hydrolysate to form a treatedlignocellulosic hydrolysate having a second concentration of the atleast one inhibitor;

providing a propagation medium comprising at least a portion of thetreated lignocellulosic hydrolysate, wherein the at least onemonosaccharide is at a concentration up to 2.0 wt % of the propagationmedium;

growing a first cell mass of the microorganism on the propagation mediumto form a second cell mass of the microorganism, wherein the second cellmass of microorganism is greater than the first cell mass of themicroorganism; and

adding a portion of the lignocellulosic hydrolysate to the propagationmedium and growing the second cell mass of microorganism to form a thirdcell mass of the microorganism, wherein the portion of thelignocellulosic hydrolysate includes the at least one inhibitor at thefirst concentration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a flow diagram of propagation and fermentation according toan embodiment.

FIG. 2 shows a flow diagram of propagation and fermentation according toan embodiment.

FIG. 3 is a graphical representation of glucose consumption duringpropagation according to an embodiment.

FIG. 4 is a graphical representation of xylose consumption duringpropagation according to an embodiment.

FIG. 5 is a graphical representation of propagation as determined byplating according to an embodiment.

FIG. 6 is a graphical representation of glucose consumption duringfermentation according to an embodiment.

FIG. 7 is a graphical representation of xylose consumption duringfermentation according to an embodiment.

FIG. 8 is a graphical representation of ethanol production duringfermentation according to an embodiment.

FIG. 9 is a graphical representation of glucose consumption duringpropagation according to an embodiment.

FIG. 10 is a graphical representation of xylose consumption duringpropagation according to an embodiment.

FIG. 11 is a graphical representation of propagation as determined by alive cell concentration according to an embodiment.

FIG. 12 is a graphical representation of glucose consumption duringfermentation according to an embodiment.

FIG. 13 is a graphical representation of xylose consumption duringfermentation according to an embodiment.

FIG. 14 is a graphical representation of ethanol production duringfermentation according to an embodiment.

DETAILED DESCRIPTION

As used herein, the term “ethanologen” refers to a microorganism thatcan convert one or more monosaccharides (e.g., glucose and the like)into at least ethanol.

As used herein the term “lignocellulosic hydrolysate” refers to acomposition that includes oligosaccharides, monosaccharides, and otherproducts including one or more inhibitors that result from the breakdownof lignocellulosic starting materials. The hydrolysate can be brokendown physically, thermally, chemically, enzymatically or combinationsthereof.

As used herein the term “lignocellulosic” refers to material comprisingboth lignin and cellulose. Lignocellulosic material may also comprisehemicellulose.

As used herein the term “cellulosic” refers to composition comprisingcellulose and additional components, including hemicellulose.

As used herein the term “saccharification” refers to the production offermentable sugars from polysaccharides.

As used herein the term “inhibitor” refers to one or more compounds thatcan reduce or otherwise affect propagation, fermentation, or both.Non-limiting examples include acetic acid, furfural,5-hydroxymethylfurfural (HMF), and combinations thereof.

As used herein the term “fermentable sugar” refers to oligosaccharidesand monosaccharides that can be used by microorganism in a fermentationprocess.

As used herein the term “fermentation” refers broadly to the enzymaticand anaerobic breakdown of organic substances by microorganisms toproduce fermentation products such as alcohols.

Disclosed are compositions, methods, and systems for propagatingmicroorganism such as yeast. For example, propagation can be used toreproduce an initial (e.g., “starter”) population of a microorganism soas to generate a larger population of the microorganism, namely increasecell numbers, that is sufficient for use in fermentation and to make afermentation product such as alcohol. Exemplary process flow diagramsare illustrated in FIGS. 1 and 2. The disclosed compositions, methodsand systems may also be used to generate or increase the amount of themicroorganism population, which may be collected and dried for use as anutritional or feed supplement or for other purposes.

As shown in FIG. 1 lignocellulosic materials are treated (e.g. by acidhydrolysis) to result in a hydrolysate. The hydrolysate is furthertreated to remove or reduce at least one or more inhibitors resulting ina treated hydrolysate.

In some embodiments, a portion of a hydrolysate is used for propagationwhereas the remaining larger volume of the hydrolysate is used forfermentation. In some embodiments, a portion of a first or secondhydrolysate as shown in FIG. 2, is used for propagation and theremaining larger volume of the first or second hydrolysate is used forfermentation. In other embodiments, the hydrolysate used for propagationis different from the hydrolysate used for fermentation.

Carbon Source

As used herein, a “carbon source” refers to one or more compounds thatinclude at least one carbon atom and can be used by a microorganism suchas yeast to grow and/or reproduce to create additional biomass.Exemplary carbon sources include monosaccharides such as glucose,fructose, galactose, mannose, xylose and the like; disaccharides such aslactose, maltose, sucrose, cellobiose and the like; oligosaccharides;polysaccharides such as cellulose, hemicelluloses, starch, xylane andthe like; single carbon substrates including only one carbon atom suchas methanol; and polyols such as glycerol, but not limited thereto.

In some embodiments, the carbon source comprises, consists essentiallyof, or consists of lignocellulosic hydrolysate. In some embodiments, thelignocellulosic hydrolysate is the entire carbon source, with no othercarbon source added. In some embodiments, if a carbon source other thanlignocellulosic hydrolysate is present, it is present in an amount thatdoes not result in the Crabtree effect.

In some embodiments, a carbon source can include in addition to thelignocellulosic hydrolysate, a carbon source from fermentation processessuch as stillage. In embodiments, the total carbon source in thepropagation medium that may be present does not exceed 2 weight percentof the total propagation medium. Therefore, if lignocellulosichydrolysate is able to provide a desirable carbon level, e.g. up to 2 wt% of total propagation medium, then in embodiments only lignocellulosichydrolysate is used as the carbon source in the propagation medium. Ifadditional carbon source is required to achieve a desirable carbon levele.g. up to 2 wt % of the total propagation medium or any other desiredamount, other carbon sources may be supplied. In some embodiments, othercarbon sources include stillage, thin stillage or combinations thereof.In some embodiments, if the medium needs further supplementing,additional carbon such as glucose may be added. In some embodiments, thecarbon source is lignocellulosic hydrolysate. In embodiments, the carbonsource present in a propagation medium ranges from 0.1 wt % to 2.0 wt %of the propagation medium, from 0.1 wt % to 1.5 wt %; from 0.2 wt % to1.5 wt % or from 0.5 wt % to 1.5 wt %.

In some embodiments, the monosaccharide present in propagation mediumranges from 0.1 wt % to 2.0 wt % of the propagation medium, from 0.1 wt% to 1.5 wt %; from 0.2 wt % to 1.5 wt % or from 0.5 wt % to 1.5 wt %.

In some embodiments the propagation medium includes one or moreinhibitors from about 1000 ppm or less, from 500 ppm or less, from 200ppm or less. In some embodiments, the inhibitors are from 1000 ppm to700 ppm, 750 ppm to 500 ppm, 600 ppm to 400 ppm, 500 to 200 ppm, from500 to 150 ppm, from 300 to 100 ppm or from 200 to 1000 ppm in thepropagation medium.

The yeast introduced to be propagated is initially at a range from 0.001wt % to 0.05 wt % of the weight of the propagation medium.

In embodiments, the propagation medium includes at least one inhibitorat a concentration of about 150 ppm to 500 ppm; and at least onemonosaccharide at a concentration from about 0.1% wt to 1.5 wt % of thepropagation medium with yeast from about 0.001 to 0.05 wt %.

In some embodiments the yeast introduced to be propagated initially inthe propagation medium includes one or more inhibitors from about 1000ppm or less, from 500 ppm or less, from 200 ppm or less. In someembodiments, the inhibitors are from 1000 ppm to 700 ppm, 750 ppm to 500ppm, 600 ppm to 400 ppm, 500 to 200 ppm, from 500 to 150 ppm, from 300to 100 ppm or from 200 to 1000 ppm in the propagation medium.

Hydrolysate

In embodiments the starting material from which a lignocellulosichydrolysate may be formed may include, for example, cellulose,lignocellulose, hemicellulose or the like. Additionally, the startingmaterial from which the hydrolysate is obtained may be sourced from anysuitable biomass or agricultural source (some nonlimiting examples ofwhich include corn stover, corn cobs, bagasse, grasses, wood and otheragricultural materials). Some nonlimiting examples of suitablehydrolysates include mixtures of different sugars, for example glucose,xylose, arabinose, cellobiose, galactose and/or fructose. In someembodiments, the hydrolysate may further include other substances suchas ethanol, glycerol, furfural, hydroxymethylfurfural (HMF), one or moreacids, for example one or more organic acids such as lactic acid andacetic acid and the like.

In some embodiments, the hydrolysate can be provided as part of or theentire carbon source in an amount so as to help reproduce (propagate) adesired population of a microorganism (e.g., ethanologen) within adesired amount of time.

In some embodiments, the hydrolysate can be a “whole broth” hydrolysateor a fraction thereof. As used herein a whole broth hydrolysatecomposition refers to a product of biomass hydrolysis and includes asolid component and a liquid component. In some embodiments, the solidcomponent can include solid, unhydrolyzed materials of a biomassfeedstock such as lignin, cellulose, and/or hemicellulose. In someembodiments, the liquid component can be a liquid hydrolysate (orliquor) and can include water, sugar and byproducts of hydrolysis suchas fermentation inhibitors. Examples of fermentation inhibitors includefurfural, hydroxymethylfurfural (HMF), phenol compounds, mixturesthereof, and the like. In some embodiments, a whole broth hydrolysateincludes at least pentose, furfural, cellulose and/or hexose, andlignin. A whole broth hydrolysate can have a total solids (dissolved andsuspended solids) content in the range from 10 to 30 percent, from 12 to25 percent, or even from 13 to 20 percent.

How to Make a Hydrolysate Composition

Hydrolysis of polysaccharides in biomass can occur by a wide variety oftechniques such as contacting the biomass with hot water, acid, base,enzyme(s), and the like.

Hydrolyzing lignocellulosic substrates to provide, e.g., xylose and/orglucose is described in, e.g., U.S. Pat. No. 5,424,417 (Torget et al.);U.S. Pat. No. 6,022,419 (Torget et al.); and U.S. Pat. No. 8,450,094(Narendranath et al.), and U.S. Publication Number 2010/0233771(McDonald et al.), wherein the entireties of said patent documents areincorporated herein by reference for all purposes.

Hydrolysis can create byproducts that can be inhibitory to downstreamprocesses such as enzymatic saccharification of polysaccharide and/oroligosaccharide material and/or downstream fermentation ofmonosaccharides. Examples of such inhibitory byproducts from hydrolysisinclude acetic acid from ester hydrolysis of acetyl groups on xylan andlignin; phenolic compounds derived from lignin hydrolysis; and/orfurfural and 5-hydroxymethylfurfural (HMF), which can be produced by thedehydration of pentoses and hexoses, respectively.

Before hydrolysis, a lignocellulosic feedstock can be prepared by avariety of techniques such as size reduction, steaming, combinations ofthese, and the like. Lignocellulosic feedstock can be prepared prior tohydrolysis such as by grinding the lignocellulosic feedstock in one ormore grinders into ground solids to reduce the size of the feedstock andincrease its surface area for contact with a hydrolysis medium.

Acid Hydrolysis

Acid hydrolysis can, for example, convert hemicellulose in the biomassinto one or more pentoses such as xylose. In some embodiments, the acidhydrolysis includes contacting lignocellulosic biomass with an aqueouscomposition to hydrolyze at least a portion of the lignocellulose intoone or more oligosaccharides and/or one or more pentoses, hexoses orboth, and forms a first hydrolysate composition including at leastpentose, cellulose, lignin, and furfural. In some embodiments, acidhydrolysis hydrolyzes at least a portion of cellulose into glucose.

During acid hydrolysis, the “severity” can be adjusted by varying one ormore of time period, temperature, and pH of hydrolysis. In someembodiments, during hydrolysis an aqueous composition can have a pH inthe range from 1 to 5, or even 2 to 3. The aqueous composition caninclude an acid such as sulfuric acid present in a concentration in therange from 0.2 to 1.3% w/w, or even 0.5 to 1% w/w. In some embodiments,acid hydrolysis can be performed for a time period in a range from 15minutes to 5 hours, or even 30 minutes to 4 hours. In some embodiments,acid hydrolysis can be performed at a temperature in the range fromgreater than 100° C. to 170° C., or even from 110° C. to 150° C.

Acid hydrolysis can be performed in a variety of system and apparatusconfigurations. In some embodiments, an acid hydrolysis system caninclude a first reactor system in fluid communication with a source oflignocellulosic biomass and a source of an aqueous composition. Thefirst reactor system can include at least one reactor configured tocontact the lignocellulosic biomass with the aqueous composition tohydrolyze at least a portion of the hemicellulose into one or moreoligosaccharides and/or one or more pentoses, and form a firsthydrolysate composition including at least pentose, cellulose, lignin,and furfural.

Optional Steam Explosion

Optionally, the first hydrolysate from acid hydrolysis can be subjectedto steam explosion conditions that make the cellulose in the firsthydrolysate more accessible during enzymatic hydrolysis. In someembodiments, steam explosion also forms furfural. Steam explosion can beperformed in a system that includes at least one reactor configured toreceive the hydrolysate and subject the cellulose in the hydrolysate toa steam explosion process under conditions that form a steam-exploded,hydrolysate composition including at least cellulose, lignin, andfurfural.

During steam explosion, cellulose (either in a hydrolysate orhydrolysate with a portion of xylose liquor removed) can be subjected toa relatively elevated pressure and temperature so that moistureimpregnated within the cellulose network is in a liquid state. Then, thepressure can be reduced so that the liquid “flashes” to a gas state sothat the sudden expansion with the cellulose network causes at least aportion of the cellulose structure to rupture, thereby increasing thesurface area of the cellulose for increased exposure to cellulaseenzymes. In some embodiments, the superheated hydrolysate compositioncan be flashed to a reduced pressure by continuously discharging thecomposition through an orifice. In some embodiments, a hydrolysatecomposition including cellulose can be subjected to a temperature in therange from 320° F. to 400° F. and a pressure in the range from 75 psigto 235 psig, followed by suddenly exposing the hydrolysate compositionto a reducing pressure such as atmospheric pressure. In someembodiments, a hydrolysate composition including cellulose can besubjected to a temperature in the range from 350° F. to 385° F. and apressure in the range from 120 psig to 195 psig, followed by suddenlyexposing the hydrolysate composition to a reducing pressure such asatmospheric pressure.

Depending on the amount of inhibitors present in the carbon source orother sources, inhibitor such as furfural or HMF can be stripped fromthe steam-exploded hydrolysate using a stripping device to inject a gasinto the hydrolysate and recover a gas that includes at least a portionof the stripped inhibitor.

In embodiments, after steam explosion, an inhibitor such as furfural canbe stripped from the steam-exploded hydrolysate using a furfuralstripping device to inject a gas into the hydrolysate and recover a gasthat includes at least a portion of the stripped furfural. Gas strippingof an inhibitor such as furfural is further discussed in PCTInternational Application Publication No. WO 2017/201233, which entireapplication is incorporated herein by reference.

In embodiments, first hydrolysate from acid hydrolysis can be separatedprior to steam explosion into a xylose liquor stream and a solidcomponent stream including at least cellulose and lignin. The xyloseliquor can be separated from the solid component after hydrolysis viaone or more of centrifugation, filtering, and the like. The solidcomponent stream can be subjected to steam explosion conditions to makethe cellulose in the solid component stream more accessible duringenzymatic hydrolysis. Advantageously, by separating at least a portionof the xylose from the cellulose into a liquor stream, the xylose in theliquor stream can avoid steam explosion condition so that such xylose isnot converted to furfural. Nonetheless, steam explosion of the cellulosein the solid component stream can still create furfural due a residualamount of xylose that may remain in solid component stream.

In an embodiment, steam explosion can be performed in a steam explosionsystem that is in fluid communication with a separation system (notshown). The separation system can be coupled to the acid hydrolysissystem to separate the first hydrolysate into the xylose liquor streamand the solid component stream. After steam explosion, the solidcomponent stream and the xylose liquor stream can be recombined andsubjected to enzymatic hydrolysis.

Enzymatic Hydrolysis

After acid hydrolysis and optional steam explosion, at least a portionof the cellulose in the hydrolysate composition can be enzymaticallyhydrolyzed to hydrolyze the cellulose into glucose. In some embodiments,at least a portion of the cellulose in the first hydrolysate compositionprovided directly from acid hydrolysis can be enzymatically hydrolyzedto form a second hydrolysate composition that includes at least pentose(e.g. xylose), hexose (e.g. glucose), lignin, and furfural.

In some embodiments, enzymatic hydrolysis can include liquefying(liquefaction) at least a portion of the cellulose in the hydrolysatefollowed by saccharifying (saccharification) at least a portion of theliquefied cellulose to form glucose. Liquefaction can include adding oneor more cellulase enzymes to the hydrolysate composition to liquefy atleast a portion of the cellulose.

A liquefaction system can include one or more vessels (not shown)containing a hydrolysate and configured to maintain the hydrolysate at apH and temperature for a time period to convert at least a portion ofthe cellulose in the lignocellulosic biomass into an oligosaccharideand/or a monosaccharide. In some embodiments, the temperature of thehydrolysate during at least a portion of liquefaction is in a range from45° C. to 65° C., or even from 50° C. to 60° C. In some embodiments, thepH of the hydrolysate during at least a portion of liquefaction is in arange from 4 to 6, or even from 4.5 to 5.5. In some embodiments, theliquefaction time period is in the range from 2 to 20 hours, or evenfrom 6 to 8 hours.

Saccharification is in fluid communication with the liquefaction system.In some embodiments, a saccharification system can include at least onereactor configured to receive the liquefied cellulose so as tosaccharify at least a portion of the liquefied cellulose and formglucose. A saccharification system can include one or more batchreactors (not shown) in fluid communication with the liquefaction system225 to receive the liquefied cellulose. The saccharification system canbe configured to maintain a hydrolysate at a pH and a temperature for atime period to convert at least a portion of the cellulose in thelignocellulosic biomass into an oligosaccharide and/or a monosaccharide.In some embodiments, the temperature of the hydrolysate can be in arange from 45° C. to 65° C., or even from 50° C. to 60° C. In someembodiments, the pH of the hydrolysate can be in a range from 4 to 6, oreven from 4.5 to 5.5. In some embodiments, the saccharification timeperiod is in the range from 48 to 120 hours, or even from 112 to 114hours.

In addition to a carbon source, a non-carbon source or nutrient sourcemay also be included to help propagate microorganisms such asethanologens. As used herein, a “non-carbon source” refers to one ormore materials or nutrients that can be used by a microorganism to growand/or reproduce to create additional microorganisms and is differentfrom a carbon source. In embodiments, the non-carbon source or nutrientscan be used as a carbon source.

In embodiments, the propagation media can include non-carbon sources ornutrients. In embodiments a stillage component (e.g. whole stillage,thin stillage and/or syrup) may be added to the propagation medium. Inembodiments, stillage provides a nutrient source in the propagationmedium.

Whole stillage is well-known and is a byproduct of distilling afermentation product. For example, a well-known process for making wholestillage is a corn grain-to-ethanol process. Grain such as corn, barley,wheat, and/or sorghum is prepared in system so that it can be fermentedinto a fermentation product that includes one or more biochemical suchas ethanol. Either the whole grain can be used or only one or moreportions of the grain can be used. For example, whole grains forfermentation are milled or fractionated into one or more separatedportions before milling. After milling, the milled grain material can befurther processed to break down polysaccharides and/or oligosaccharidesinto one or more monosaccharides such as glucose that can be fermentedby, e.g., yeast. Methods of breaking down polysaccharides such as starchinto glucose are well known and include e.g. hot water, such as hotwater that includes an added acid such as sulfuric acid, and/orenzymatic pretreatment or simultaneous saccharification andfermentation. After fermentation, the fermentation product is distilledin a system, where the ethanol is removed from the fermented mash in adistillation column. After the ethanol is removed, the remaining residueis removed as stillage residue. The stillage residue is known as “wholestillage.” The whole stillage can be optionally further processed viaone or more systems to further clarify or separate the whole stillagebefore being delivered to propagation system. For example, the wholestillage can be subjected to a solid-liquid separation process toproduce a solid stream of residue, also known as wet cake, and a liquidstream of residue, also referred to as thin stillage. The thin stillagecan be further processed to increase the solids concentration byevaporation resulting in condensed distillers solubles or syrup.Typically the syrup is mixed back with the separated solid stream or wetcake and fed to a dryer to remove the remaining moisture. The resultingdry solids are referred to as Dried Distillers Grains and Solubles or“DDGS”, and can be sold as animal feed.

Such stillage component from the grain-to-ethanol producing process,including the whole stillage, wet cake, thin stillage, and/or syrup canbe used as at least part of the non-carbon source for propagatingmicroorganisms such as yeast. Using at least a portion of the wholestillage provides an alternative or additional non-carbon source ascompared to, e.g., yeast extract. Using whole stillage or thin stillageas the entire amount of nutrients or part of the nutrients can propagateyeast as well as, or better than, other non-carbon sources such as yeastextract.

In some embodiments, the non-carbon source includes a stillage componentsuch as thin stillage, wetcake, syrup, and any combination thereof. Thenon-carbon source can include syrup derived from thin stillage, thinstillage, or combinations thereof. In some embodiments, the nutrientsource can include known nitrogen sources such as yeast extract andurea.

The stillage component can be provided in any amount so as to helpreproduce (propagate) and generate a desired population of microorganism(e.g., ethanologen) within a given amount of time. The amount ofstillage component provided can depend on factors such as the type andamount of other non-carbon sources present, the type and amount ofcarbon sources present, pH, temperature, desired time period forpropagation, and the like. In some embodiments, the non-carbon source isprovided only as a stillage component such as thin stillage.

In some embodiments, stillage is added to the propagation medium ataround 10-35 wt % of the propagation medium. In other embodiments, thestillage is added at about 20-30 wt % the propagation medium. In someembodiments, the stillage component (e.g. thin stillage) contains lessthan 5000 mg/L of acetic acid, less than 8000 mg/L of lactic acid orboth. In some embodiments, the non-carbon source includes thin stillagebut no yeast extract, urea or both. In some embodiments, additionalnutrients are supplied in addition to stillage. In some embodiments, thenon-carbon source includes yeast extract, urea or both.

Propagating a microorganism that can convert one or more monosaccharidesinto a biochemical will be described below by reference to anethanologen such as genetically modified yeast for making ethanol. Thepresent disclosure, however, is not limited to propagating only suchyeast and it should be understood that propagating any othermicroorganism (e.g. genetically modified or non-genetically modified) iscontemplated.

Propagating a microorganism (e.g. an ethanologen includes combining afirst cell mass of the microorganism with at least a hydrolysatecomposition to facilitate growth of a sufficient amount of ethanologen(i.e. ethanologen second cell mass) for inoculation (i.e. ethanologeninoculum to be supplied) to a fermentation system. The first cell massof the microorganism (e.g., ethanologen) can be included either whilethe medium is being formed, after the medium is formed, or both.

According to an exemplary embodiment the propagation medium for thepropagation system includes a carbon source including hydrolysate, anon-carbon source having stillage as all or part of the non-carbonsource, and, optionally, one or more additional agents (not shown).

Optional additional agents for propagating yeast are well known andinclude, e.g., agents supplied with an ethanologen such as antibiotics,supplemental or accessory enzymes, materials for adjusting andmaintaining pH, nutrients or other components providing nutritional orother benefits to the microorganism. Optional additional nutrientsinclude, e.g., yeast extract, urea, diammonium phosphate, magnesiumsulfate, zinc sulfate or other salts, and the like.

The ratio of non-carbon source to carbon source is selected to grow adesired cell mass of microorganism such as a sufficient size cell massof yeast for fermentation in a cellulosic ethanol process. Factors inselecting the ratio of non-carbon source to carbon source include thetype(s) and amount(s) of non-carbon sources, the type(s) and amount(s)of carbon sources, types and amounts of additional propagation mediumagent(s), the types and initial amounts of microorganisms, the timeperiod targeted for growing the microorganism, pH, temperature, and thelike. Additional considerations include whether it is desired tocondition the microorganisms during propagation to the environmentexpected during fermentation. Conditioning microorganisms to thefermentation environment can advantageously help the microorganismsoperate (e.g., convert sugar to ethanol) more effectively.

Propagating the microorganism can begin when the microorganism ispresent in the propagation medium and desired conditions are present.Conditions to consider for propagation of a microorganism include, e.g.,amount of ingredients, pH, time period for growth of the microorganism,stir speed (if stirring is present), exposure to oxygen, temperature,and the like.

In some embodiments, the first cell mass (e.g., initial cell mass) ofthe microorganism is present in an amount less than 5 grams ofethanologens per liter of medium, less than 2 grams of ethanologens perliter of medium, or less than 0.5 grams of microorganism per liter ofmedium. In some embodiments, the first cell mass of the microorganism isfrom 0.5 to 1 grams of microorganism per liter of medium. In someembodiments, the first cell mass of the microorganism is from 0.05 to 2grams of microorganism per liter of medium, 0.05-0.5 grams ofmicroorganism per liter of medium.

The cell mass can be propagated, depending on conditions, for a time toproduce a desired cell mass. Typically, the desired cell mass is a sizesufficient to ferment sugar into an alcohol (e.g., ethanol) within aneconomically desirable time period. Exemplary time periods include from12-80 hours, 24-48 or 48-80 hours. In exemplary embodiments, the desired(e.g., second or final) cell mass of the microorganism (e.g. yeast) ispresent in an amount in the range from 10 to 1000 times the initial orfirst cell mass of the microorganisms, 200-1000 times, 300 to 800,500-1000 times; 100-1000 times; 10 to 30 times the initial or first cellmass of the microorganisms, from 20-30 times or 15 to 25 times, or from15 to 35 times the initial or first cell mass of the microorganisms. Inembodiments the second cell mass of the organism is grown within a timeperiod in the range of from 8 to 80, from 12-48 hours, from 12-24 hoursor from 12 to 60 hours, wherein the time period begins when the firstcell mass of the microorganism is combined with the carbon source topropagate the first cell mass of the microorganism.

The pH of the propagation medium can be at a pH that helps reproduce(propagate) and generate a desired population of microorganism (e.g.,ethanologen) within a desired amount of time. In some embodiments, thepH is between 4 and 8, between 5 and 7, or between 4.5 and 6. Techniquesfor adjusting and maintaining pH of a propagation medium for propagatingmicroorganisms such as an ethanologen are well known and include, e.g.,adding one or more acidic materials and/or adding one or more basicmaterials.

The temperature of the propagation medium can be at a temperature thathelps reproduce (propagate) and generate a desired population ofmicroorganism (e.g., ethanologen) within a desired amount of time. Insome embodiments, the temperature is at a temperature in the range offrom 15° C. to 50° C., from 20° C. to 40° C., or from 25° C. to 40° C.or 20-37° C.

In some embodiments the second or final cell mass of the microorganismis present in an amount in the range of from 10-30 times the initial orfirst cell mass within a time period in the range of from 12 to 48hours, at a pH from about 4-6 and at a temperature from 20-30° C.

Propagation of a microorganism can be performed according to acontinuous process, fed-batch process, a batch process, or combinationsthereof. Preferably, batch process has certain benefits associatedtherewith. A batch process can be highly desirable as it can berelatively easier to manage and control as compared to a continuous orfed-batch process.

In some embodiments, the propagation medium is stirred, or oxygen isotherwise added, for at least a portion of the propagation process so asto provide sufficient oxygen levels throughout the medium so as topromote aerobic respiration and, therefore, reproduction of themicroorganism instead of, e.g., anaerobic fermentation production ofethanol. In some embodiments, if sufficient oxygen is not provided tothe propagation medium, the process can switch to an anaerobic pathwayand promote fermentation so as to produce alcohol to an undue degree.

Also disclosed is a propagation system in which in embodiments,propagation is performed in one or more stages. For example, where yeastis the microorganism to be propagated, the propagation system caninclude at least two stages. In a first stage, a yeast culture can begrown into an initial yeast inoculum. In the first propagation stage,the initial yeast inoculum is introduced into a vessel and diluted (e.g.by 250×). In the vessel, the initial yeast inoculum and a portion of thecarbon source (e.g., treated hydrolysate), a portion of the non-carbonsource (e.g., thin stillage), and water may be supplied along withoptional additional agents (discussed above). According to exemplaryembodiments, the temperature may be maintained in a range of about 26 to37 degrees Celsius and the pH in a range of about 3.5 to 6.5 for a timeof at least 24 hours. For example, yeast can be grown in the firstpropagation stage under conditions including a temperature of about 30degrees Celsius and a pH of about 5.5 for about 24 hours.

In the second propagation stage, the yeast inoculum from the firstpropagation stage is diluted (e.g. by 10×), typically after beingtransferred to another vessel. In the vessel, the yeast inoculum fromthe first propagation stage and a portion of the carbon source, aportion of the non-carbon source, and water may be supplied along withoptional additional agents (discussed above). According to exemplaryembodiments, the temperature may be maintained in a range of about 26 to37 degrees Celsius and the pH in a range of about 3.5 to 6.5 for a timeof at least 24 hours. For example, yeast can be grown in the secondpropagation stage under conditions comprising a temperature of about 30Celsius and a pH of about 4.5 to about 5.5 for about 24 hours.

According to an embodiment, the yeast cell mass will grow by about 200to 500 fold in the first stage and about 20 to 40 fold in the secondstage.

After propagation, cell mass of microorganism is provided to afermentation system so as to ferment a biomass such as pretreatedlignocellulosic material and produce ethanol.

In some embodiments, the yeast propagated on treated hydrolysate after aperiod of time is further grown or propagated on hydrolysate, namelyhydrolysate that is not stripped of inhibitors such as furfural and thelike. The un-treated hydrolysate or hydrolysate is added to thepropagation vessel for an additional one to 3 hours under conditionsused to propagate the microorganisms. Without being bound by any theory,this exposure of already-propagated microorganism to hydrolysate that isnot further stripped of inhibitors “adapts” or “conditions” themicrograms before exposing the microorganism to fermentation conditions.

In some embodiments, microorganisms (e.g. yeast) that have beenpropagated from an initial or first cell mass of microorganism to asecond cell mass of microorganisms can be further grown for anadditional time period to produce a third cell mass of microorganisms.In embodiments, the second cell mass of microorganisms are grown on ahydrolysate composition comprising inhibitors from about 500 ppm to 4200ppm, from 600 ppm to 4000 ppm, 500 to 3500 ppm. In embodiments theinhibitors include furfural at 500 ppm to 4200 ppm, from 600 ppm to 4000ppm, 500 to 3500 ppm. In embodiments, the second cell mass ofmicroorganisms are “conditioned” after a period of propagation for about1 to 3 hours, from 1-2 hours or 2-3 hours at 20-30° C. and at a pH from5 to 6.

In some embodiments, the first cell mass of the microorganism is from0.01 to 1 grams of microorganism per liter of medium that is propagatedon a lignocellulosic hydrolysate that includes 2000 ppm or less ofinhibitor and at least one monosaccharide at a concentration from 0.1 wt% to 2 wt % of the hydrolysate. The first cell mass is grown for 12-72hours and a pH from 4-7 to result in the second cell mass of themicroorganism which is in the range of 5 to 500 times the initial orfirst cell mass of the microorganism.

The resultant microorganisms that are propagated by the describedmethods are used to convert, namely ferment, a carbon source to adesired bio product. In embodiments, the microorganisms are grown onfermentable sugars to convert sugar into ethanol. The microorganismsused for fermentation are microorganisms that have been propagated bythe methods described herein or by microorganisms that are further“conditioned.”

When microorganisms are exposed to inhibitors greater than the inhibitorconcentrations present at propagation, such microorganisms are found toresult in an increase in fermentation. In some embodiments, the increasein fermentation is an increase in the consumption of fermentable sugars.In embodiments, microorganisms that are exposed to greater sugar,inhibitors, or both showed better fermentation rates compared tomicroorganisms propagated as fed-batch with around 1 to 2 wt %monosaccharides and around 100-300 ppm inhibitors medium.

Microorganisms

Microorganisms that can convert one or more monosaccharides into abiochemical or fermentation product are well known and include, e.g.,bacteria and/or fungi such as yeast. The biochemical can vary dependingon the conditions that are provided. In many embodiments, thebiochemical includes biofuels such as ethanol, butanol, and the like. Insome embodiments, the microorganism includes one or more ethanologenicmicroorganisms referred to as “ethanologens”.

The microorganism to be propagated and later used for fermentationinclude prokaryotic (e.g. bacteria) and eukaryotic (e.g. yeast, fungiand algae) microorganisms. Exemplary bacterial microorganisms includethe genera Escherichia, Bacillus, Klebsiella, Lactobacillus,Lactococcus, and the like. Exemplary algae include the genus Chlorella,Thraustochytriu, Schizochytrium, Crypthecodinium, and the like. In someembodiments, the algae are heterotrophic algae.

Exemplary yeast and fungus include the genus of, Aspergillus, Candida,Pichia, (Hansenula), Phanerochaete, Kloeckera (Hanseniaspora),Kluyveromyces, Rhodotorula, Torulopsis, Zygosaccharomyces, Yarrowia, andSaccharomyces.

In some embodiments, the microorganisms include Escherichia coli,Klebsiella oxytoca, Zymomonas mobilis, Clostridium thermocellum, Pichiapastoris, Pichia stipites, Candida albicans, Saccharomyces cerevisiae,Phanerochaete chrysosporium Schizosaccharomyces pombe, and/or Yarrowiahpolytica.

In some embodiments, the microorganism to be propagated includesgenetically modified yeast such as genetically modified Saccharomycescerevisiae. According to one embodiment, the yeast is a strain ofSaccharomyces cerevisiae yeast. In some embodiments, the yeast is astrain of Saccharomyces cerevisiae capable of converting, namelyfermenting, glucose, xylose, arabinose or a combination thereof. In someembodiments, the yeast is a genetically modified strain of Saccharomycescerevisiae yeast capable of growing on hydrolysate or treatedhydrolysate. In still other embodiments, the yeast strain is anon-genetically modified strain (e.g. Saccharomyces cerevisiae).

Suitable yeasts include any of a variety of commercially availableyeasts, such as commercial strains of Saccharomyces cerevisiae availableunder the trade names, e.g., Ethanol Red® from LeSaffre or TransFerm®from Mascoma Corporation. Exemplary yeast strains can ferment xyloseand/or glucose into an alcohol such as ethanol. For example, a usefulstrain of yeast includes Saccharomyces cerevisiae yeast altered toconvert (i.e., ferment) xylose and glucose to ethanol (i.e., agenetically modified yeast derived from an organism as described in U.S.Pat. No. 7,622,284). As another example, a useful strain of yeastincludes Saccharomyces cerevisiae yeast altered (i.e., geneticallymodified) to convert (i.e., ferment) xylose, arabinose, and glucose toethanol.

Additional embodiments include the following:

-   1. A method of propagating a microorganism, the method comprising:-   a) providing a first propagation medium comprising a carbon source    component, the carbon source component comprises at least a    lignocellulosic hydrolysate comprising at least one monosaccharide    and at least one inhibitor at a concentration of about 1000 ppm or    less, wherein the at least one monosaccharide is at a concentration    from about 0.1 wt % to 2.0 wt % of the propagation medium; and-   b) growing a first cell mass of the microorganism on the propagation    medium to form a second cell mass of the microorganism, wherein the    second cell mass of microorganism greater than the first cell mass    of the microorganism.-   2. The method as in embodiment 1, wherein the first cell mass of the    microorganism is from about 0.001 wt % to 0.05 wt % of propagation    medium.-   3. The method as in any one of the preceding embodiments, wherein    the at least one inhibitor comprises furfural,    5-hydroxymethylfurfural (HMF) or combinations thereof.-   4. The method as in any one of the preceding embodiments, wherein    providing the carbon source comprises:-   a) forming a lignocellulosic hydrolysate composition comprising at    least one inhibitor greater than 1000 ppm; and-   b) reducing the at least one inhibitor to less than 1000 ppm.-   5. The method as in embodiment 4, wherein the reducing is by    dilution or gas stripping or both.-   6. The method as in any one of embodiments 4-5, wherein the gas    stripping is by with air, nitrogen, ozone or combinations thereof.-   7. The method as in any one of the preceding embodiments, wherein    the second cell mass of the microorganism comprises 100 to 1000    times the first cell mass of microorganisms.-   8. The method as in any one of the preceding embodiments, wherein    the second cell mass of the microorganism comprises 10-30 times the    cell mass of microorganisms.-   9. The method as in any one of the preceding embodiments, wherein    the propagation medium further comprises a non-carbon source.-   10. The method as in any one of the preceding embodiments, wherein    the non-carbon source comprises a by-product of fermenting a grain    material.-   11. The method as in any one of the preceding embodiments, wherein    the by-product of fermenting a grain material comprises stillage    component.-   12. The method as in any one of the preceding embodiments, wherein    the stillage component is thin stillage.-   13. The method as in any one of the preceding embodiments, wherein    substantially no ethanol is produced by the first cell mass of the    microorganism or second cell mass of the microorganism during the    growing time period.-   14. The method as in any one of the preceding embodiments, wherein    the second cell mass of the ethanologens is present in an amount in    the range of from 10 times to 30 times the first cell mass within a    time period from 12 hours to 48 hours, wherein the time period    begins when the first cell mass of the ethanologens is combined with    the propagation medium to propagate the first cell mass of the    ethanologens grown at about 20° C. to 37° C. at pH from about 4 to    6.-   15. The method as in any one of the preceding embodiments, wherein    the method further comprises growing the second cell mass of    microorganism on a carbon source having an inhibitor concentration,    or monosaccharide concentration or both greater than the first    carbon source to form a third cell mass of the microorganism.-   16. The method as in any one of the preceding embodiments, wherein    the microorganism comprises yeast.-   17. The method as in any one of the preceding embodiments, wherein    the yeast comprises genetically modified yeast.-   18. The method as in any one of the preceding embodiments, wherein    the yeast is Saccharomyces cerevisiae.-   19. The method as in any one of the preceding embodiments, wherein    the yeast is capable of growing on glucose, xylose, arabinose or a    combination thereof.-   20. The method as in any one of the preceding embodiments further    comprising using the second cell mass of the microorganism or the    third cell mass of microorganism or combinations thereof to ferment    a fermentable sugar to produce a fermentation product.-   21. The method as in any one of the preceding embodiments, wherein    the fermentation product is ethanol.-   22. A system for propagating a microorganism comprising:-   (a) a propagation reactor vessel, wherein the propagation reactor    vessel contains a propagation medium comprising a carbon source, the    carbon source comprising:

i) at least a lignocellulosic hydrolysate;

ii) at least one monosaccharide at a concentration from about 0.1 wt %to 2.0 wt % of the propagation medium; and

iii) at least one inhibitor at a concentration of about 1000 ppm orless; and

-   (b) a first cell mass of microorganism; wherein the propagation    reactor vessel is configured for growth of the first cell mass of    microorganism to form a second cell mass of microorganism, wherein    the second cell mass of the microorganism is greater than the first    cell mass of the microorganism; and-   (c) an aerator coupled to the propagation reactor vessel.-   23. A method of increasing fermentation rate comprising:-   a) providing a propagation medium comprising a first carbon source,    the first carbon source comprising;

i) at least a lignocellulosic hydrolysate;

ii) at least one monosaccharide at a concentration from about 0.1 wt %to 2.0 wt % of the propagation medium; and

iii) at least one inhibitor at a concentration of about 1000 ppm or lesspropagation medium; and

-   b) growing a first cell mass of the microorganism on the propagation    medium to form a second cell mass of the microorganism, wherein the    second cell mass of microorganism is greater than the first cell    mass of the microorganism;-   c) providing a second carbon source comprising at least one    inhibitor, a monosaccharide or both at a concentration higher than    the first carbon source;-   d) growing the second cell mass of microorganism on the second    carbon source to form a third cell mass of the microorganism; and-   e) adding the third cell mass of the microorganism with fermentable    sugars to ferment the fermentable sugars to produce a fermentation    product.-   24. The method as in embodiment 23, wherein the fermentation rate is    greater using the third cell mass compared to the second cell mass    of microorganisms.

EXAMPLE 1 Presence of Inhibitors

Slurries (referred as propagation slurry Batch 1 and Batch 2) wereobtained from a commercial lignocellulosic ethanol facility. Each slurrycontained acid pretreated and enzymatically hydrolyzed corn stover thatwere used for propagation.

Batch 1 propagation slurry contained about 724 ppm furfural, 50 ppm5-hydroxymethylfurfural (HMF), 0.38% w/v acetic acid, 1.65% w/v glucose,and 1.14% w/v xylose.

Batch 2 contained about 68 ppm furfural, 28 ppm HMF, 0.42% w/v aceticacid, 1.53% w/v glucose, and 1.16% w/v xylose.

To each batch was added grain ethanol thin stillage, and water. Thepropagation slurries were each added to 70% volume of the 6.6 L Bioflo310 bioreactor. The bioreactor was aerated and controlled at 31.1° C.and pH 5.5. Crème yeast from Novozymes was added at approximately 0.2g/L DCW. The propagation was allowed to continue until dissolved oxygenand near infrared testing showed that sugar had been consumed by theyeast (>50% xylose consumption).

Once propagation was complete, 10% by volume of the propagation slurrywas combined with 90% by volume of the similar acid pretreated andenzymatically hydrolyzed corn stover that was previously pH adjusted to5.5 in a shake flask topped with a water lock to provide thefermentation slurries. The fermentation slurries were allowed to fermentfor 72 hours at 32° C. in an air shaker incubator.

Fermentation slurries referred to as fermentation slurry Batch I andBatch II were each used for fermentation.

Fermentation slurry Batch 1 contained about 891 ppm furfural, 54 ppmHMF, 0.39% w/v acetic acid, 2.6% w/v glucose, and 1.68% w/v xylose.

Fermentation slurry Batch 2 contained about 1111 ppm furfural, HMF wasbelow the detection limit, 0.45% w/v acetic acid, 3.5% w/v glucose, and2.2% w/v xylose.

High performance liquid chromatography was used to test for sugar andethanol concentrations during both propagation and fermentation and asshown in FIGS. 3, 4, and 6-8. Propagation samples were also plated usingyeast extract, peptone, xylose, and penicillin agar plates to determinepropagation and as shown in FIG. 5.

The results show that the yeast was propagated on the compositionscontaining inhibitors and no added sugars. The resultant propagatedyeast was able to ferment the sugars to produce ethanol.

EXAMPLE 2 Different Sugar Levels with Furfural Stripping

A slurry obtained from a commercial lignocellulosic ethanol facilitycontaining acid pretreated and enzymatically hydrolyzed corn stover wasused for propagation. The acid pretreated and enzymatically hydrolyzedcorn stover was first air stripped to remove furfural and then combinedat different levels with grain ethanol thin stillage and variable waterto create different propagation slurries referred to as High Sugar,Medium Sugar, and Low Sugar.

The High Sugar propagation slurry contained about 93 ppm furfural, 73ppm HMF, 0.18% w/v acetic acid, 1.65% w/v glucose, and 1.10% w/v xylose.

The Medium Sugar propagation slurry contained about 27 ppm furfural, 19ppm HMF, 0.06% w/v acetic acid, 0.41% w/v glucose, and 0.26% w/v xylose.

The Low Sugar propagation slurry contained about 15 ppm furfural, 11 ppmHMF, 0.04 weight percent (w/v) acetic acid, 0.24% w/v glucose, and 0.14%w/v xylose.

The propagation slurries were each added to 70% volume of the 6.6 LBioflo 310 bioreactor. The bioreactors were aerated and controlled at31.1° C. and pH 5.5. The commercially available antibiotic Lactoside 247was added at 13 ppm. Active dry yeast from Novozymes was added atapproximately 0.05 g/L DCW. The propagation was allowed to continueuntil dissolved oxygen and NIR testing showed that sufficient sugar hadbeen consumed by the yeast (>50% xylose or glucose consumption). Oncepropagation was complete, 10% by volume propagation slurry was combinedwith 90% by volume of acid pretreated and enzymatically hydrolyzed cornstover previously pH adjusted to 5.5 in a shake flask topped with awater lock. The various fermentation compositions were allowed toferment for 72 hour at 32° C. in an air shaker incubator.

Each fermentation composition contained 2183 ppm furfural, 143 ppm HMF,0.29% w/v acetic acid, 3.1% w/v glucose, and 2.2% w/v xylose. Highperformance liquid chromatography was used to test for sugar and ethanolconcentrations during both propagation and fermentation as shown in FIGSFIGS. 9, 10, 12-14. Propagation samples were also tested using aNexcellom Cellometer to determine a live cell concentration and as shownin FIG. 11.

The results show that yeast propagated on higher sugar amounts resultedin higher cell concentrations and better fermentation rates.

What is claimed is:
 1. A method of propagating a microorganism, themethod comprising: providing a lignocellulosic hydrolysate comprising atleast one monosaccharide and at least one inhibitor, where the at leastone inhibitor is at a first concentration, wherein the at least oneinhibitor is a byproduct of hydrolysis of lignocellulosic biomass, andwherein the at least one inhibitor is an inhibitor of fermentation bythe microorganism; reducing the first concentration of the at least oneinhibitor in a portion of the lignocellulosic hydrolysate to form atreated lignocellulosic hydrolysate having a second concentration of theat least one inhibitor; providing a propagation medium comprising atleast a portion of the treated lignocellulosic hydrolysate, wherein theat least one monosaccharide is at a concentration up to 2.0 wt % of thepropagation medium; growing a first cell mass of the microorganism onthe propagation medium to form a second cell mass of the microorganism,wherein the second cell mass of microorganism is greater than the firstcell mass of the microorganism; and adding a portion of thelignocellulosic hydrolysate to the propagation medium and growing thesecond cell mass of microorganism to form a third cell mass of themicroorganism, wherein the portion of the lignocellulosic hydrolysatecomprises the at least one inhibitor at the first concentration.
 2. Themethod of claim 1, wherein providing the lignocellulosic hydrolysatecomprises: providing lignocellulosic biomass comprising hemicellulose,cellulose, and lignin; and hydrolyzing at least a portion of thelignocellulosic biomass to form the at least one inhibitor at the firstconcentration and a saccharide chosen from one or more oligosaccharides,the one or more monosaccharides, and combinations thereof, wherein theone or more monosaccharides are chosen from one or more pentoses, one ormore hexoses, and combinations thereof.
 3. The method of claim 1,wherein the hydrolyzing comprises contacting the lignocellulosic biomasswith hot water, and wherein the at least one inhibitor is a byproduct ofcontacting the lignocellulosic biomass with the hot water.
 4. The methodof claim 1, wherein the at least one inhibitor is a byproduct ofcontacting the lignocellulosic biomass with a treatment compositioncomprising an acid, and wherein the at least one inhibitor is abyproduct of contacting the lignocellulosic biomass with the treatmentcomposition comprising the acid.
 5. The method of claim 1, wherein theat least one inhibitor is a byproduct of contacting the lignocellulosicbiomass with a treatment composition comprising a basic, and wherein theat least one inhibitor is a byproduct of contacting the lignocellulosicbiomass with the treatment composition comprising the base.
 6. Themethod of claim 1, wherein the at least one inhibitor is chosen fromacetic acid, furfural, 5-hydroxymethylfurfural, phenolic compoundsproduced from lignin hydrolysis, and combinations thereof.
 7. The methodof claim 2, wherein providing the lignocellulosic hydrolysate furthercomprises enzymatically hydrolyzing at least a portion of the cellulosein the lignocellulosic biomass.
 8. The method of claim 2, whereinproviding the lignocellulosic hydrolysate further comprises subjectingthe lignocellulosic biomass to steam explosion.
 9. The method of claim1, wherein the second concentration of the at least one inhibitor is 500ppm or less.
 10. The method of claim 1, wherein the second concentrationof the at least one inhibitor is 200 ppm or less.
 11. The method ofclaim 1, wherein the first concentration of the at least one inhibitoris greater than 1000 ppm.
 12. The method of claim 1, wherein the firstconcentration of the at least one inhibitor is from 600 ppm to 4200 ppm.13. The method of claim 1, wherein reducing the first concentration ofthe at least one inhibitor in a portion of the lignocellulosichydrolysate comprises a process chosen from dilution, gas stripping, andcombinations thereof.
 14. The method of claim 13, wherein the gasstripping is performed with a gas chosen from air, nitrogen, ozone, andcombinations thereof.
 15. The method of claim 1, wherein the at leastone monosaccharide is at a concentration from about 0.1 wt % to 2.0 wt %of the propagation medium.
 16. The method of claim 1, wherein thepropagation medium further comprises a stillage component, wherein thestillage component is chosen from whole stillage, thin stillage, wetcake, syrup, and combinations thereof.
 17. The method of claim 1,wherein the first cell mass of the microorganism is from about 0.001 wt% to 0.05 wt % of propagation medium, wherein the second cell mass ofthe microorganism comprises 100 to 1000 times the first cell mass ofmicroorganisms, and wherein substantially no ethanol is produced by thefirst cell mass of the microorganism or second cell mass of themicroorganism during the growing.
 18. The method as in claim 1, whereinthe microorganism comprises yeast, wherein the yeast is Saccharomycescerevisiae, and wherein the yeast is capable of growing on a carbonsource chosen from glucose, xylose, arabinose, and combinations thereof.19. The method of claim 1, further comprising providing cell mass fromthe third cell mass of the microorganism to fermentation to produce afermentation product.
 20. The method of claim 19, wherein thefermentation product comprises ethanol.